Pneumatic hammers intended to work at the bottom of the hole generally comprise a tubular body supplied with compressed air, a distribution mechanism, a percussion piston, and a bit receiving the blows of the percussion piston in order to transmit them to the rock. The percussion piston is movable in a cylinder formed by a liner, and longitudinal passages are provided between the liner and the inside wall of the hammer body for the supply of the compressed air acting on the piston, while other passages serve to exhaust the air after it has acted on one face or the other of the percussion piston.
In order to enable the percussion piston to apply sufficient striking force to the bit, and consequently to the rock which is being drilled, use is made of compressed air under high pressure, for example 20 to 25 bars. The consumption, which may be of the order of 10 to 15 cubic meters at S.T.P., for example, therefore entails the use of high-output, high-pressure compressors, i.e., heavy and bulky equipment. Moreover, this equipment is expensive, both with regard to initial cost and immobilization of capital and with regard to operating costs, because of the considerable consumption of energy.